Make it optional if proxivocab details should be included in exports

[JohannesLipp]

1. Add a new download icon right to the existing one, which downloads the vocab with proxivocab information (please use a second icon for that OR create a popup with two buttons "Normal Download" and "Proxivocab Enhanced")
2. Update the behavior of the existing ("normal") download button so that it download the vocab without proxivocab information